It appears you're asking how to apply for either TSA Precheck for domestic travel or Global Entry (GOES), for domestic and international travel, which includes TSA Precheck, as well. If you travel internationally at all, GOES is a better choice, as the fee is only $15 additional ($100) over the $85 for TSA Precheck, alone.

Following are the links you can go to, to apply for TSA Precheck or Global Entry; just follow all the directions: